A fuel and air mixture is combusted within cylinders of an internal combustion engine. Reciprocating pistons are moved between top dead center and bottom dead center positions within the cylinders by a crankshaft situated in a crankcase of the engine. As each piston moves toward its top dead center position, it compresses the fuel and air mixture. When the compressed mixture combusts, it expands and drives the piston downward toward its bottom dead center position. Combustion within the cylinder releases energy and generates combustion products and by-products, most of which are exhausted from the cylinder into an exhaust system of the engine during the exhaust phase of the combustion cycle. However, some of the combustion products and/or by-products enter into the crankcase by blowing past seal rings around the pistons, and are thus termed “blow-by gases” or simply “blow-by.”
Blow-by gases contain contaminants normally found in the engine's exhaust such as, for example, hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), soot, and unburned or partially burned fuel. In addition, because the crankcase is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may mix with and entrain oil droplets and oil vapor.
As blow-by gases build up in the crankcase, they must be vented to relieve pressure in the crankcase. Some systems vent the blow-by gases directly to the atmosphere. However, the contaminants in blow-by gases may be harmful to the environment. Therefore, emissions concerns make direct atmospheric venting a poor option under most, if not all, operating conditions. To minimize the negative effects on the environment, engine manufacturers have routed crankcase emissions to either the engine intake or to the exhaust line upstream of emission control devices. The result was a new emissions flow path.
Problems arose in routing crankcase emissions to the exhaust line. In some instances, there is a pressure imbalance between the intake system, the exhaust system, and the crankcase. Instead of the crankcase emissions venting through the exhaust system to the tailpipe, the pressure imbalance causes oil and exhaust to flow back into the engine via the crankcase. This blowby of the exhaust/air mixture into the engine cylinder can negatively work against piston movement.
One method that has been implemented by engine manufacturers to prevent an improper balance of exhaust versus crankcase pressures is described by U.S. Patent Application Publication 2007/0084194 (the '194 publication) by Holm, published on Apr. 19, 2007. The '194 publication discloses a crankcase ventilation system including an exhaust gas conduit through which exhaust gas flows from an engine, and a crankcase emissions conduit through which crankcase emissions flow from the engine. The exhaust gas conduit includes a crankcase emissions inlet through which the crankcase emissions flow from the crankcase emissions conduit into the exhaust gas conduit. The exhaust gas conduit includes a reduced portion having a minimum inner diameter, the minimum inner diameter being located downstream of the crankcase emissions inlet for drawing the crankcase emissions through the inner diameter. In this manner, the system of the '194 publication eliminates the pressure imbalance between the exhaust system and the crankcase for certain pre-determined conditions.
Although the system of the '194 publication may be adequate for some situations, it may have limited applicability. Specifically, the reduced portion provides a constant pressure drop in the exhaust conduit. As such, the system of the '194 publication may be unable to adjust to varying pressure conditions between the crankcase and exhaust system. This lack of versatility may render the system of the '194 publication unable to adjust to a variety of pressure conditions, thereby increasing the likelihood of improper engine operation.
The present disclosure is directed to overcoming one or more of the problems set forth above.